The present invention relates to a feedforward amplifier in which distortion occurring when a multifrequency multiplexed signal of a high frequency band is amplified is suppressed to produce only a main amplified signal.
For feedforward amplifiers, various circuit configurations have been proposed, but the configurations become complex, which has soared the production cost of the amplifier. FIG. 12 shows a circuit layout example of a feedforward amplifier of the prior art.
The feedforward amplifier of FIG. 12 includes a distortion detecting loop A and a distortion removing loop B. In the loop A, an input signal from an input terminal 301 is a multifrequency multiplexed signal of a high frequency band. The input signal is simultaneously amplified by a main amplifier 304. A nonlinear distorted signal component resultant from the amplification by the main amplifier 304 is detected by canceling the amplified input signal components. In the distortion removing loop B, the distorted signal component detected by the loop A is amplified by a subordinate amplifier 315. The amplified signal is mixed with an output signal which includes a distorted signal component and which is outputted from the main amplifier 304. This cancels the distorted signal component in the output signal from the main amplifier 304 to obtain only the amplified input signal component.
The distortion detecting loop A includes a directional coupler 319, a two-output distributor 302, a vector adjuster 303, a main amplifier 304, a delay line 306, a controller 309, and a detector circuit 322. The loop A further includes couplers 307 and 308, which are shared between the loops A and B.
Operation of the distortion detecting loop A will be described. The directional coupler 319 mixes the multifrequency multiplexed signal received from the input terminal 301 with a single-frequency pilot signal. The mixed signal is distributed by the two-output distributor 302 as a first output and a second output. The first output is delivered via the vector adjuster 303 to the main amplifier 304, which resultantly produces an output signal. The coupler 308 mixes a part of the output signal with the second output signal which is outputted from the two-output distributor 302 and which has passed the delay line 306. These signals having mutually opposite phases.
The detector circuit 322 detects the pilot signal in the mixed signal. To minimize a signal level of the pilot signal component from the detector circuit 322, the controller 309 controls the vector adjuster 303 to adjust quantity or values of attenuation and phase. When the controller 309 appropriately controls the vector adjuster 303, the coupler 308 outputs only the distorted signal resultant from the amplification of the main amplifier 304.
Description will now be given of operation of the distortion removing loop B. In the coupler 312, the distorted signal detected by the distortion detecting loop A is received as a first input via the vector adjuster 313 and the subordinate amplifier 315. The coupler 312 receives as a second input the output signal from the main amplifier 304 delayed through the delay line for a propagation delay time of the vector adjuster 313 and the subordinate amplifier 315. The first and second input signals have opposite phases.
The coupler 912 mixes these signals with each other and feeds a resultant mixed signal to a coupler 316. The coupler 316 delivers a part of the mixed signal to a detector circuit 323. The detector circuit 323 detects a pilot signal component of the input signal and outputs the pilot signal component to a controller 314. To minimize a level of the pilot signal component, the controller 314 controls the vector adjuster 313 to adjust quantity of attenuation and phase. Therefore, when the controller 314 controls the vector adjuster 313 in an appropriate manner, the coupler 316 outputs only the input signal component amplified by the main amplifier 304.
To implement the function, each of the distortion detecting loop A and the distortion removing loop B of the feedforward amplifier of the prior art includes a pilot oscillator (318, 320) a controller (309, 314) and a detector circuit (322, 323).
However, the feedforward amplifier of this configuration requires a large number of elements and hence a high production cost. Consequently, various feedforward amplifiers of a simplified circuit configuration have been proposed.
Japanese Patent Laid-Open Publication No. Heisei 6-244647 describes an example of a feedforward amplifier of the prior art. As shown in FIG. 13, the feedforward amplifier includes a switching unit S at an output terminal of a spread spectrum (SS) pilot signal oscillator 401 to deliver pilot signals to couplers 408 and 409. Namely, the pilot signal oscillator 401 is shared between a distortion detecting loop and a distortion removing loop.
The feedforward amplifier further includes a controller 407 to receive output signals respectively from couplers 411 and 410. The controller 407 receives a pilot signal component in a mixed signal from the coupler 411 and a pilot signal component in a mixed signal from the coupler 410. To minimize a reception level of each of the pilot signal components, the controller 407 controls a distortion detecting vector adjuster 404 and a distortion removing vector adjuster to adjust magnitude of amplitude and phase.
In the feedforward amplifier of the prior art, the distortion detecting loop and the distortion removing loop share the pilot signal oscillator 401 and the controller 407. To achieve the function of the feedforward amplifier shown in FIG. 13, this amplifier is more simplified in the circuit configuration when compared with that of FIG. 12.
In the feedforward amplifier configured as shown in FIG. 13, the pilot signal oscillator and the controller are shared between the distortion detecting loop and the distortion removing loop. Therefore, the feedforward amplifier includes two output terminals to deliver pilot signals from the pilot signal oscillator, and the controller includes two input terminals to receive mixed signals.
When the pilot signal oscillator 401 outputs a pilot signal from a first output terminal, a leakage signal of the pilot signal appears on a second output terminal of the oscillator 401. When a mixed signal is delivered to a first input terminal of the controller 407, a leakage signal of the mixed signal takes place on a second input terminal of the controller 407.
Consequently, the mixed signal propagating through the circuit includes an inherent pilot signal component and a leakage pilot signal component having a frequency equal to that of the inherent pilot signal component. The controller detects both of these signals to control the vector adjusters 404 and 405. This naturally leads to a control error.
In this connection, the feedforward amplifier of the prior art shown in FIG. 13 includes a spread spectrum (SS) pilot signal. Therefore, the control error due to the signal leakage between two output terminals and between two in t terminals is small enough for the controller 407 to appropriately control the distortion detecting vector adjuster 404 and the distortion removing vector adjuster 405.
However, when the single frequency pilot signal described in conjunction with FIG. 12 is applied in place of the spectrum spread pilot signal to the feedforward amplifier in which the distortion detecting loop and the distortion removing loop share the pilot signal oscillator and the controller as shown in FIG. 13, the control error in the adjustment of the quantity of attenuation and phase in the vector adjusters becomes greater when compared with a case in which the spectrum spread (SS) pilot signal is employed. Consequently, there arises a problem of insufficient improvement in the removal of the distorted signal. This problem is not taken into consideration in the prior art shown in FIG. 13.
It is therefore an object of the present invention to provide a feedforward amplifier with a simplified configuration to share a pilot signal oscillator and a controller between a distortion detecting loop and a distortion removing loop. In the feedforward amplifier, two output terminals for the pilot signal oscillator are sufficiently isolated from each other as well as tow input terminals of the controller are also fully isolated from each other. This suppresses the signal leakage between two output terminals and between two input terminals and hence leads to satisfactory improvement sufficient to remove the distorted signal.
In accordance with first aspect of the present invention, there is provided to achieve the object above, a feedforward amplifier, comprising:
a main amplifier,
a distortion detecting loop for detecting a nonlinear distorted signal component appearing due to amplification of a multifrequency input signal by said main amplifier and
a distortion removing loop for removing a distorted signal component from the multifrequency input signal amplified by said main amplifier, according to the distorted signal component detected by said distortion detecting loop;
a pilot signal oscillating means for alternately outputting a pilot signal for a detecting operation of a distorted signal component of said distortion detecting loop and a removing operation of a distorted signal component of said distortion removing loop; and
a detecting means for alternately receiving mixed signals from said distortion detecting loop and said distortion removing loop and detecting a pilot signal component in the mixed signals received from said loops, wherein:
said pilot signal oscillating means includes output change-over means for outputting the pilot signal to either one of said distortion detecting loop and said distortion removing loop, said output change-over means including a multistage change-over switch; and
said detecting means includes input change-over means for receiving the mixed signal from either one of said distortion detecting loop and said distortion removing loop, said input change-over means including a multistage change-over switch.
In accordance with second aspect of the present invention, there is provided to a feedforward amplifier, comprising:
a main amplifier,
a distortion detecting loop for detecting a nonlinear distorted signal component appearing due to amplification of a multifrequency input signal by a main amplifier and
a distortion removing loop for removing a distorted signal component from the multifrequency input signal amplified by said main amplifier, according to the distorted signal component detected by said distortion detecting loop;
a pilot signal oscillating means for alternately outputting a pilot signal for a detecting operation of a distorted signal component of said distortion detecting loop and a removing operation of a distorted signal component of said distortion removing loop; and
a detecting means for alternately receiving mixed signals from said distortion detecting loop and said distortion removing loop and detecting a pilot signal component in the mixed signals received from said loops, wherein:
said pilot signal oscillating means includes output change-over means for outputting the pilot signal to either one of said distortion detecting loop and said distortion removing loop, said output change-over means including a multistage change-over switch;
said detecting means includes input change-over means for receiving the mixed signal from either one of said distortion detecting loop and said distortion removing loop, said input change-over means including a multistage change-over switch and;
said output change-over means comprises:
a first change-over switch for connecting the pilot signal to either one of two output terminals;
at least one stage of a second change-over switch disposed for each pair of two output terminals of said first change-over switch for connecting the pilot signal delivered from said first change-over switch to an input of a change-over switch in a succeeding stage or to ground; and
a third change-over switch disposed for each pair of two output terminals of said second change-over switch for connecting the pilot signal fed from said second change-over switch to an output terminal of said pilot signal oscillating means or to ground.
In accordance with third aspect of the present invention, there is provided to a feedforward amplifier, comprising
a main amplifier,
a distortion detecting loop for detecting a nonlinear distorted signal component appearing due to amplification of a multifrequency input signal by a main amplifier and
a distortion removing loop for removing a distorted signal component from the multifrequency input signal amplified by said main amplifier, according to the distorted signal component detected by said distortion detecting loop;
a pilot signal oscillating means for alternately outputting a pilot signal for a detecting operation of a distorted signal component of said distortion detecting loop and a removing operation of a distorted signal component of said distortion removing loop; and
a detecting means for alternately receiving mixed signals from said distortion detecting loop and said distortion removing loop and detecting a pilot signal component in the mixed signals received from said loops, wherein:
said pilot signal oscillating means includes output change-over means for outputting the pilot signal to either one of said distortion detecting loop and said distortion removing loop, said output change-over means including a multistage change-over switch;
said detecting means includes input change-over means for receiving the mixed signal from either one of said distortion detecting loop and said distortion removing loop, said input change-over means including a multistage change-over switch; and
said output change-over means comprises:
a change-over switch in a preceding stage for connecting an output of the pilot signal to either one of two output terminals; and
a change-over switch in a succeeding stage disposed for each pair of the two output terminals of said second change-over switch in the preceding stage for connecting the pilot signal outputted from the change-over switch in the preceding stage to an output terminal of said pilot signal oscillating means or to ground.
In the first to third aspects of the present invention, said input change-over means comprises:
first change-over switch in a preceding stage disposed for each pair of two input terminals of said detecting means for connecting the input signal to an input terminal of a change-over switch in a preceding stage or to ground; and
a second change-over switch disposed in a succeeding stage of said first change-over switch in the preceding stage for connecting one of outputs from said change-over switch in the preceding stage to an input terminal of said detecting means are preferable.
In the first to third aspects of the present invention, said input change-over means comprises:
first change-over switch disposed for each pair of two input terminals of said detecting means for connecting the signal inputted thereto to an input terminal of a change-over switch in a subsequent stage or to ground;
at least one stage of a second change-over switch disposed for each pair of two output terminals of said first change-over switch for connecting a signal inputted from said first change-over switch to an input of a change-over switch in a succeeding stage or to ground; and
a third change-over switch for connecting either one of outputs from said second change-over switch to an input terminal of said detecting means are preferable.
In accordance with fourth aspect of the present invention, there is provided to a feedforward amplifier, comprising:
a main amplifier;
a distortion detecting loop for detecting a nonlinear distorted signal component appearing through amplification of a multifrequency input signal by said main amplifier;
a distortion removing loop for removing a distorted signal component from the multifrequency input signal amplified by said main amplifier, according to the distorted signal component detected by said distortion detecting loop;
pilot signal oscillating means for alternately outputting a pilot signal for a detecting operation of a distorted signal component of said distortion detecting loop and a removing operation of a distorted signal component of said distortion removing loop; and
detecting means for alternately receiving a mixed signal from said distortion detecting loop and said distortion removing loop and detecting a pilot signal component in the mixed signal received from said loops, wherein:
said pilot signal oscillating means includes output change-over means for outputting the pilot signal to either one of said distortion detecting loop and said distortion removing loop;
said output change-over means is disposed for each pair of two output terminals of said pilot signal oscillating means and includes an isolator to guarantee isolation between the two output terminals and a change-over switch disposed in a stage preceding said isolator to connect an output of a pilot signal to either one of said isolators;
said detecting means includes input change-over means for receiving the mixed signal from either one of said distortion detecting loop and said distortion removing loop; and
said input change-over means is disposed for each pair of two input terminals of said detecting means and includes an isolator to guarantee isolation between the two input terminals and a change-over switch disposed in a stage succeeding said isolator to connect an output from either one of said isolators to an input terminal of said detecting means.
In accordance with fifth aspect of the present invention, there is provided to a feedforward amplifier:
a directional coupler for mixing an input multifrequency multiplexed signal inputted thereto with a pilot signal received via a first output terminal of said output change-over means from said pilot signal oscillating means;
a two-output distributor for dividing the mixed signal into tow output signals;
a first vector adjuster for receiving the first output signal from said two-output distributor and for adjusting quantity of phase and quantity of attenuation of the first output signal;
a main amplifier for amplifying an output signal from said first vector adjuster;
a first coupler for separating a part of an amplified signal from said main amplifier and for outputting therefrom the signal separated from the amplified signal;
a first delay line for delaying propagation of a second output signal from said two-output distributor for a propagation time of a signal in said main amplifier and said first vector adjuster;
a second coupler for mixing a signal delayed by the first delay line with a signal received from said first coupler, the delayed signal having a phase opposite to that of the signal received from said first coupler;
a third coupler for separating a part of a mixed signal from said second coupler and for outputting therefrom the signal separated from the mixed signal;
a control circuit for receiving an output signal from said third coupler via a first input terminal of said input change-over means and for controlling quantity of phase and quantity of attenuation in said first vector adjuster, thereby minimizing a level of a pilot signal component detected in said output signal from said third coupler by said detecting means;
a fourth coupler for mixing, after the control operation is conducted for said first vector adjuster by said control circuit, a pilot signal received via a second output terminal of said output change-over means from said pilot signal oscillating means with an output signal from said first vector adjuster;
a second vector adjuster for receiving a signal obtained by mixing by said second coupler a part of a signal attained by amplifying by said main amplifier a mixed signal from said four coupler with a signal delayed by said delay line and received by said second coupler and for adjusting quantity of attenuation and quantity of phase of the signal from said second coupler;
a subordinate amplifier for amplifying an output signal from said second vector adjuster;
a second delay line for delaying propagation of a signal for which a pilot signal have been mixed by said four coupler and which has been outputted from said main amplifier for a propagation time of a signal in said second vector adjuster said subordinate amplifier;
a fifth coupler for mixing a signal delayed by said second delay line and received therefrom with a signal received from said subordinate amplifier, the delayed signal having a phase opposite to that of the signal from said subordinate amplifier, and for outputting a mixed signal resultant from the mixing to an output terminal; and
a sixth coupler for separating a part of the signal fed to the output terminal and for outputting the separated signal therefrom, wherein:
said input change-over means receives the output signal from said sixth coupler via a second input terminal; and
said control circuit adjusts quantity of attenuation and quantity of phase of said second vector adjuster to minimize a level of a pilot signal component detected by the detecting means in a signal received via a second input terminal.
In the first to fifth aspects of the present invention, said change-over switches include transfer switches are preferable.
In the first to fifth aspects of the present invention, said pilot signal oscillator means produces a pilot signal having a frequency of about 2 GHz.
In the first to fifth aspects of the present invention, said pilot signal is a signal having a single frequency.